Answer:
number of terms=9
Step-by-step explanation:
[tex]t_{1}=6\\t_{5}=18\\\\t_{n}=t_{1}+(n-1)d\\18=6+(5-1)d\\18-6=4d\\4d=12\\d=12/4=3\\s_{n}=162\\s_{n}=\frac{n}{2}[2t_{1}+(n-1)d]\\162=\frac{n}{2}[2(6)+(n-1)3]\\162 \times 2=n(12+3n-3)\\324=n(3n+9)\\3n^2+9n-324=0\\n^2+3n-108=0\\n^2+12n-9n-108=0\\n(n+12)-9(n+12)=0\\(n+12)(n-9)=0\\n=-12,9\\n=-12 (rejected)[/tex]
as number of terms can't be negative.
